Method and composition for coating pre-sized paper with a mixture of a polyacid and a polybase

Abstract

The present invention features coating compositions and methods for improving the quality of images printed on a paper substrate. The novel coating compositions contain a coating agent comprising a mixture of a polyacid and a polybase. When applied to a sized paper substrate, the coating compositions provide a coated paper substrate that provides high quality printed images when printed with an ink containing a reactive dye having ionizable and / or nucleophilic groups capable of reacting with the coating agent. Images printed on a paper substrate coated with the coating composition of the invention are bleed-resistant, water-resistant (e.g., water-fast), and / or are characterized by an enhanced chroma and hue.

Description

The present invention relates generally to the production of coated paper, and more particularly relates to a novel paper coating process and novel compositions useful in conjunction therewith.As printing technology advances, paper manufacturers are faced with the increasingly rigorous demands of their customers for high quality paper that is economically attractive. For example, there is a keen demand for papers that meet high quality standards with respect to brightness, opacity, and dry and / or wet strength, and that, upon printing with any of a wide range of colorants, provide a water-resistant printed image. The customer further demands that such papers be amenable to use with a variety of printing techniques, including not only conventional printing techniques, but also "impact free" printing techniques such as inkjet printing (particularly colored inkjet printing), laser printing, photocopying, and the like.In response, paper manufacturers have attempted to meet their customer...

AI Technical Summary

Benefits of technology

The present invention is based upon the discovery that a composition containing a coating agent comprising a mixture of a polyacid and a polybase is effective in coating a sized paper substrate to provide numerous advantages. Coated paper substrate that has been treated with a coating composition of the invention yields high quality printed images having improved color fastness (the printed images do not run when exposed to moisture) as a result of the substantially non-reversible binding of aqueous colorants to the coating agent present in the coating composition. These images are therefore characterized as "water-resistant" or "water-fast" due to the characteristics of the printed image following exposure to water.

The coated paper substrates of the invention can be used in conventional printing, or with digital printing (particularly inkjet printing, including drop-on-demand printing and continuous printing) to provide highly brilliant, printed images that are significantly improved in color quality (for example, with respect to chroma and hue) when compared to uncoated paper substrates and / or to paper substrates coated with conventional coating compositions. The coating compositions and their methods of use according to the present invention thus provide a number of advantages over conventional sizing and coating methods, and sizing and coating compositions.

The coating compositions of the invention can be readily prepared from commercially available starting materials and / or reagents, are compatible with additional binders or additives, can be used with a variety of base papers, and are compatible with a variety of printing methods, including conventional and digital printing methods (particularly inkjet printing, including drop-on-demand printing and continuous printing), and can also be used with existing commercial paper production processes and equipment. The coating composition is inexpensive to prepare, and relatively small amounts are required to provide a coated paper substrate having the advantageous features described herein. The coating compositions of the invention are also easy to handle due to their solubility in water (the active components, the coating agents, are hydrophilic polymers), and do not require the use of large volumes of organic solvents. The novel coating compositions herein also possess good film-forming properties.

The coated paper substrate prepared using the composition of the invention exhibits improved durability, as evidenced by improved paper strength (e.g., tear strength), and stability upon prolonged storage. The coated paper does not discolor or yellow, and maintains a high degree of brightness for extended periods of time. Paper substrates treated with the coating compositions of the invention react rapidly and, in some embodiments, irreversibly with a number of aqueous based colorants, thus providing a versatile coating system for use with a wide variety of available colorants. Furthermore, because the colorant reacts quickly with the coating compositions, the coated printed substrate does not require a separate curing step, but rather is fast-drying. This fast-drying characteristic provides for printed images that are "non-sticky," thus allowing the printed coated paper substrate to be handled immediately after printing, e.g., to allowing stacking. The coated paper substrate of the invention can also be used to prepare images with varying degrees of gloss, depending upon variations in pigment.

The coating composition layer can range in thickness from several hundred Angstroms to several mils in thickness, e.g., in the range of approximately 100 Angstroms to 5 mm; typical amounts of the coating composition to be applied generally range from about 50 to about 500 pounds per ton of substrate, or about 2 to 30 g / m.sup.2. In one embodiment, the coating composition is applied so that it does not substantially infiltrate into the substrate (e.g., the substrate is of a porosity such that the coating composition does not substantially penetrate beyond or far beyond the substrate surface). Application of a coating in a selected thickness can readily be done by one of skill in the art using known techniques, for example, by varying the coating agent concentration and number of coatings and through selection of the application means.

Problems solved by technology

Although these materials are effective to various degrees under certain conditions, use of each is associated with certain limitations.

However, the opacity and brightness of the paper substrate decrease in direct proportion to the amount of sizing agent applied to the paper.

Moreover, as the amount of sizing agent and / or the cost of the sizing agent increases, the cost of producing the paper increases, making high quality papers prohibitively expensive.

Certain sizing agents impart relatively poor bleed resistance and water resistance of imprinted inks, and thus must be used with insolubilizing agents to ensure production of a printed paper having satisfactory water resistance.

However, while starches may provide improved porosity, these compounds generally do not provide for improved bleed resistance or water resistance of inks printed on the treated paper substrates.

However, synthetic sizing agents tend to be expensive, due to both the cost of the starting material and the amount that is required to provide a paper substrate having the desired characteristics.

Use of conventional sizing agents normally results in a decrease in the porosity of the final paper substrate; thus, while the sized paper substrate may have the desired brightness and opacity, it may not provide for a printed image having a suitable optical density or color intensity.

If the porosity of the paper is too high, the paper is too stiff for handling by automated industrial devices for folding and sorting (e.g., devices of the "suction extractor" type) during envelope production.

In contrast to lower porosity papers, high porosity papers also require slower machine speeds, and further require refining and draining operations that have relatively high energy costs.

Both of these requirements result in decreases in plant productivity, efficiency, and cost effectiveness.

These additional steps translate to additional manufacturing costs.

Moreover, the components of such conventional coating compositions are often quite expensive, further adding to production costs.